1. Field of the Invention
The present invention relates to a sensor device which includes a bridge circuit made up of detection elements whose resistance values change in accordance with external forces and converts changes in the resistance values to electrical signals, and a method for adjusting such sensor devices.
2. Description of Related Art
Conventionally, one well-known device of this type is a sensor device which uses a pressure detection unit that includes a Wheatstone bridge formed with piezoresistance elements whose resistances change in accordance with an external force.
This device generates a detection signal detected by the bridge circuit after amplifying the same signal using an amplifier so that the output signal is at a signal level at which it can be used by a controller that performs control using the output signal of this device and this device has a predetermined sensitivity in correspondence with the external force.
Also, if the gain of the amplifier fluctuates for some reason, because such fluctuation adversely affects controllability, that is, excessive sensitivity results in over-sensitive control and conversely, insufficient sensitivity results in slower control and the like, there is a need to check for such abnormal sensitivity. This is done, for example, by providing a determination circuit which determines an abnormality when the output voltage from the sensor device exceeds an upper limit of the signal level that can be handled by the controller.
However, in such controller equipped with a determination circuit, there is a problem of being able to perform abnormality detection only when the gain increases resulting in an over-sensitive device and not when sensitivity deteriorates.
Moreover, in order to perform detection of deteriorating sensitivities, there are known devices, for detecting abnormality, having sensor units are doubled and the like so that pressure is detected using a plurality of systems with abnormality detection being performed by comparing the outputs of the sensor units. However, in this case, the increased size of such devices poses a problem.